Common Sense Media
This is a site that I found a couple month ago and I have come to really rely on it. It is a site that reviews everything media including movies, games, website, etc. The site reviews media specifically for parents that want to make sure they know what their kids are seeing.
The reason I have some to trust this site over many others, is the detail with which the site writes its reviews. Common Sense includes in their reviews what the movie is about and the age appropriateness like many others. Though it also rates the degree of educational value, positive messages, positive role models, violence & scariness, sexy stuff, language, consumerism, and drugs & drinking. Then with each individual rating it gives detailed explanations for those ratings. Such as with language, they tell each of the words that were used in the movie.
I know that I don't have kids yet but I have found this site to be a great resource to steering clear of some questionable movies. Ones that I would rather not see.
Common Sense Media, check it out!